(57) A speech coding system is shown, which comprises a linear transform unit (50) for
executing linear transform on an input signal (Si) with a predetermined block length
(Sb) and an FFT unit (10, 30) for executing Fast Fourier transform on the input signal
(Si) with two different, i.e., large and small, block lengths, a block length setting
unit (20) for calculating a predetermined block length (Sb) to be set in the linear
transform unit (50) according to an FFT signal generated in the FFT unit (10, 30)
and setting this block length in the linear transform unit (50), and a coding unit
(80) for coding an intermediate signal (Sm) generated in the linear transfom unit
(50) to form and output a bit stream (So). The FFT unit has a function of selecting
a block length used for the Fast Fourier transform among two, i.e., large and small,
block lengths according to a continuous portion of the input signal (Si).
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